Compared with historically accumulated hydrographic and nutrients measurements taken at
sea, total inorganic carbon dioxide (TCO2) data are far from enough to produce a gridded map
ping of high resolution on a global scale, which is crucial to evaluate the carbon budget in the
oceans and provide initial values to constrain the biochemical models. In order to get a better
understanding of TCO2in the oceans and contribute the large historical database to TCO2estima
tion, TCO2 properties and its relation with nutrients in the world oceans are presented and dis
cussed using ship data from several international programs, especially recent WOCE cruises dur
ing which the accuracy of TCO2 measurements are believed to have been significantly improved.
Based on these, a new parameterization method is proposed and tested to estimate TCO2 below
the upper oceans (＞ 400 m) where its seasonal variations are comparatively small. Compared with
the ship data which have not been involved in the parameterization procedure, the mean bias and
standard deviation are 0.8 u.mol/kg and 7.0 u.mol/kg respectively for Pacific Ocean, while they are
0.5 u.mol/kg and 5.4 u.mol/kg respectively for Atlantic Ocean. Calculated TCO2 in the global
oceans can be obtained at Levitus grid point (1°x1°) from 400 m down to the depth of 5,500 m,
including vast ocean areas where field investigations ofTCO2 have never been performed.
The mortality of the Japanese littleneck clam (Ruditapes phillippinarum), caused by a decline
in bottom dissolved oxygen (DO) concentration, in the shallow muddy bottom of Mikawa Bay,
was measured throughout a 50 day period during the early summer of 1996.
Using that data, it was attempted to compute the change in mortality as a function of change in
When the percentage of DO saturation was considered as the only factor affecting mortality, it
did not fit the observed mortality, however it did fit when water temperature was included as an
Decline of the standing stock of macro-benthos and meio-benthos in the same area was well
represented by this mortality function. It was also suggested that meio-benthos mortality in lower
temperature than 25 degree is larger than that of macro-benthos.
Wehave developed a multi-sensor, salinity/temperature measurement system based on the XCTD
(Expendable Conductivity, Temperature & Depth Profiling System). The system utilizes five
modified XCTD probe as its CT sensors. Each CT sensor is connected with a 500m long multiwire
cable at intervals of 50 m, and the cable is connected at its end to a measurement control and
data logging system consisting of a notebook computer and peripheral components on land. The
CT sensors are installed on the bottom of brackish water lakes and tidal rivers. The CT sensors are
switched on in turn by computer control, and the measurement of conductivity and temperature is
carried out. Salinity is calculated using measured conductivity and temperature data recorded
inside the computer.
The system has following features.
(1) On-line system. The system allows to get measurement data in real time.
(2) Digital system. Digital output data of the CT sensor can transmit on the cable of maximum
10 km length.
(3) The sensors have high sensitivity and accuracy.
(4) Low cost sensors are used.
As the results of observation experiment carried out for two months in River Gonokawa and
Lake Nakaumi located in western part of Honshu, Japan, salinity and temperature data were suc
cessfully obtained. The system could detect the movement of the salt water in a tidal river and a
We developed a prototype of a dynamic positioning buoy using DGPS (Differential Global
Positioning System). The research budget provided by the Science and Technology Agency of the
Japanese Government (the Special Coordination Founds) since 1993. The research is principally
aimed at developing of oceanographic vertical observation buoy system to keep the position within
a specific area, such as a drifting warm-core ring.
The prototype buoy, 5.4m in length, is made of aluminum alloy. A nutrient analysis sensor,
sensor for primary production and winch system with cable for vertical sensing are installed in the
buoy. Buoy position is self-controlled by using DGPS position data and self-propulsion unit with
three electric thrusters. DGPS correction data and position data of the buoy are transmitted via
communication satellite. Electric power is supplied by solar and lithium batteries.
We carried out full scale trials with significant wave height about 1.4 m, average wind velocity
about 5m/sec, buoy drifting velocity about 0.27 m/sec. Dynamic positioning performance and con
trolling ability of the vertical sensing system of the buoy are confirmed by these experiments.
Changes in the nitrogen budget between the sediment and overlying water, were evaluated using
a benthic ecosystem model for the shallow area of Mikawa bay, Japan. The model was run for the
period between June to July (1996) when a water mass, severely deficient in dissolved oxygen,
developed and resulted in drastic benthic community changes.
The model result indicated that the nitrogen budget changed greatly as a dissolved oxygen defi
cient water mass developed. The shallows had the capability of reducing the particulate organic
nitrogen at higher efficiency than the rate of elution of dissolved inorganic nitrogen when ambient
oxygen conditions were normal. But, After the oxygen deficient water mass developed, the re
moval rate of particulate organic nitrogen decreased with the death of macrobenthic suspension
feeders more rapidly than the elution rate in dissolved inorganic nitrogen and consequently, the
budget of total nitrogen swinged from sink to source.
It is very important to keep the dissolved oxygen saturation level that the benthicfauna can
survive to maintain the water purification capacity of the shallows.
In order to evaluate the influence of shellfish farming on water quality, a hydrodynamical and
ecological coupled model was applied to Chinhae Bay. We compared results of simulations that
included and excluded the presence of farmed shellfishes.
From the hydrodynamic simulation, Chinhae Bay has a calm current system except at the
mouth. Bay water exchanges with open sea water through the Caduk and Central channels.
From the simulation that included farmed shellfishes, it was estimated that shellfishes ingested
34% of phytoplankton primary production (including zooplankton and detrital matter), and egested
70% of that organic matter in the form of fecal pellets. Thus according to the simulation,
farmed shellfishes reduced the standing stocks of phytoplankton, zooplankton, and POC from
water throughout the Bay by 325 tons, 19 tons, and 821 tons respectively. The phytoplankton
biomass in this simulation reduced the organic matter the produce which also means a low COD
value (concentration). In contrast, amounts of DIN and DIP increased to 508 tons and 50 tons
respectively, through fecal pellets excreted by the shellfishes. The nutrient flux from the sediment
also increased as a restul for these pellets depositing on the sea bed. For example, the DIN and
DIP flux from the sediment were approximately 10 and 2 times higher than simulations run ex
cludingshellfishes. Based on these simulation results, it appears that shellfishfarming has a great
impact on the coastal ecosystem.
A size-based ecosystem model has been developed to understand a detailed food web system
such as a micro-bial loop occurred in a coastal bay (estuary).The model is applied to TokyoBay
by coulpling with a 3-D hydrodynamical model. In this application, picoplankton, nano-diatom,
nano-flagellate, net-diatom and net flagellate are considered as compartments of autotrophic level.
Bacteria, heterotrophic flagellate, micro-zooplankton and meso-zooplankton are considered as
compartments of heterotrophic level.
According to the sensitivity tests of the model, it is found that the most sensitiveparameterin
themodel is the meso-zooplankton grazing rate. Thechange of 0.1 day1 in the meso-zooplankton
grazing rate leads to the change of 90 mgCnr3 diatom biomass. The results of the sensitivity
analysis show thatthe value of 0.8day1 forthemeso-zooplankton grazing rateis appropriate. The
simulated phytoplankton is well reproduced for the present situation inTokyo Bay.
The time variations of the simulated biomass of autotrophic components show that diurnal
variations caused byphotosynthesis arepredominant. In the heterotrohphic compartments, mesozooplankton
biomass also shows typical diurmal variations as a resultof prey-predator interac
tion. The net-diatom and net flagellate vary within the period of 10 days in the simulation, and
meso-zooplankton also varies with thesame time period but with lags lOdays behind net-phytoplankton,
which reflects on the prey-predator interaction.
In thesimulation, net-phytoplankton is dominant in the upper bay, whereas nano- and pico
plankton becomedominantnear the entranceof the bay.
This study demonstrates that the developed model can clarify the temporal and spatial varia
tions of each size category and of each trophic level.